bacterial genetics

• pros of bacteria for genetics

  • easily cultured
  • short generation time
  • haploid (only one copy of the gene, to make recombinant, so see phenotype immediately)
  • E.coli widely used
• bacteriophages of E.coli (that infect E.coli)

  • T7
  • Lambda
  • T5
  • fd
  • T4
• bacteriophages are 


  viruses that infect bacteria
• bacteriophages are structurally and functionally diverse
• virulent bacteriophage multiply and lyse bacterial cell, releasing progeny bacteriophage particle
• temperate bacteriophage can integrate into bacterial chromosome and remain dormant, replicating along with bacterial DNA
• lytic life cycle of bacteriophage

  1. sticks to receptors on outer surface of E.coli
  2. phage injects DNA into cell
  3. empty capsid remains outside cell, cell's DNA is hydrolysed
  4. cell metabolic machinery produced phage proteins and phage genome, reforming phage (head, tail and tail fibres)
  5. phage directs production o lysozymes, causing cell to swell and burst, releasing phage's that have been made
• temperate phage

  labels

  A) lytic cycle

  B) lysogenic cycle

  C) cell lyses, releasing phage

  
• mutations create new alleles
• recombination produces new combinations of alleles
• gene transfer and recombination occurs through

  1. transformation
  2. transduction
  3. conjugation
• transformation is the 


  uptake of naked DNA
• transduction

  • transfer of bacterial genes from one bacteria to another by bacteriophage
• 2 types of transduction

  • generalised (only with virulent phage)
  • specialised (occurs only with temperate phage)
• conjugation 


  ability to form sex pili and transfer DNA
• conjugation id determined by plasmid called an F factor
• conjugation

  labels

  A) F plasmid

  B) bacterial chromosome

  
• F factor is a fertility factor that determines 


  ability to form sex pili
• gene expression in bacteria is often controlled at level of

  inititation of transcription
• transcription begins when RNA polymerase binds to a promoter
• control of tryptophan biosynthesis is an example of

  regulated synthesis of repressible enzymes
• no tryptophan means the repressor is inactive so the operon is

  on
• tryptophan present means repressor is active and the operon is

  off
• tryptophan is an example of negative regulation which is 


  binding of repressor/tryptophan to operator blocks transcription
• control of lactose metabolism is an example of

  regulated synthesis of inducible enzymes
• when lactose is absent, repressor is active so the operon is

  off
• when lactose is present, repressor is inactive so the operon is

  on
• positive regulation is when 


  binding of molecule to the operator turns on gene expression
• positive regulation (lactose)

  • lactose present
  • cAMP is high, glucose is scarce
  • abundant lac mRNA synthesis
• negative regulation (lactose)

  • lactose present
  • cAMP low, glucose abundant
  • little lac mRNA synthesis